EFFECT OF CHROMIUM(VI) ON PHOTOSYSTEM II ACTIVITY AND HETEROGENEITY OF SYNECHOCYSTIS SP (CYANOPHYTA): STUDIED WITH IN VIVO CHLOROPHYLL FLUORESCENCE TESTS

Abstract

The inhibitory effect of Cr(VI) on the PSII of Synechocystis sp. was studied. Cr(VI) reduced O-2 evolution and inhibited the water-splitting system in PSII. S-states test and flash induction test showed that Cr(VI) exposure increased the proportion of inactivated PSII (PSIIX) and PSII beta reaction centers, which increased the fluxes of dissipated energy. JIP test and Q(A)(-) reoxidation test demonstrated that Cr(VI) treatment induces inhibition of electron transport from Q(A)(-) to Q(B)/Q(B)(-) and accumulation of P-680(+). More Q(A)(-) had to be oxidized through S-2(Q(A)Q(B))(-) charge recombination and oxidation by PQ9 molecules in PSII under Cr(VI) stress. These changes finally decreased the index of photosynthesis performance